In this reaction, water (H2O) is split into hydrogen (H2) and oxygen (O2) gases. During this process, the oxidation state of hydrogen changes from +1 in H2O to 0 in H2, while the oxidation state of oxygen changes from -2 in H2O to 0 in O2. Therefore, hydrogen undergoes reduction, while oxygen undergoes oxidation. Since both oxidation and reduction occur in this reaction, it is classified as a redox reaction.